1. Field of the Invention
This invention relates to an energy meter and a method of metering consumed energy. This invention is particularly applicable to the supply of energy in the form of fuel gas.
2. Discussion of the Background
Conventionally energy consumption in the form of fuel gas is determined for billing purposes by measuring the volume of gas supplied to the consumer by providing a gas flow meter at the point of delivery. The gas supplier also remotely monitors the quality of gas supplied to a distribution area occupied by the consumer using the calorific value (CV) of the gas which is the fundamental measure of energy per unit volume, generally measured with a large and expensive chromatograph. From the CV of the gas supplied to the area together with the reading of the volume of fuel gas consumed by the customer, the gas supplier is able to determine the energy consumption from which the consumer is charged.
As the customer is only able to determine the volume, of gas consumed without knowing the gas quality, he is unable to precisely monitor how much he will be charged. This is particularly disadvantageous for pre-payment xe2x80x9ccoin operatedxe2x80x9d gas meters.
According to a first aspect of the present invention an energy meter comprises:
means to measure a volume of gas supplied;
means to measure a calorific value of the gas supplied; and
means to calculate an energy value corresponding to the measured volume of gas supplied and the measured calorific value wherein both of the means to measure a volume of gas supplied and the means to measure a calorific value of the gas supplied are provided in a single integral meter unit.
According to a second aspect of the present invention a method of determining a quantity of energy supplied to a consumer comprises:
measuring a volume of gas supplied;
measuring a calorific value of the gas supplied; and
calculating an energy value of the supplied gas corresponding to the measured volume of gas supplied and the measured calorific value wherein both the measuring of a volume of gas supplied and the measuring of a calorific value of the gas supplied are performed at substantially the point of delivery to the consumer.
The provision of an energy reading at the customer,s premises enables the consumer to monitor how much he will be charged. This is especially advantageous for pre-payment meters.
According to a further aspect of the present invention an energy meter comprises:
means to measure a volume of gas supplied;
an apparatus to measure a calorific value of the gas including means to measure the speed of sound in the gas and means to use the speed of sound in an operation producing the calorific value of the gas corresponding to said speed of sound; and
means to calculate an energy value corresponding to the measured volume of gas supplied and the measured calorific value.
According to a still further aspect of the present invention a method of determining a quantity of energy supplied comprises:
measuring a volume of gas supplied;
measuring a calorific value of the gas supplied including measuring the speed of sound in the gas and using the speed of sound in an operation producing the calorific value of the gas corresponding to said speed of sound; and
calculating an energy value of the supplied gas corresponding to the measured volume of gas supplied and the measured calorific value.
The means to measure a volume of gas supplied and the apparatus to measure the calorific value of the gas are preferably provided in a single unit. The means to calculate an energy value may also be provided in the same unit but may additionally or alternatively be provided remotely, for example at the gas supplier""s billing department.
Since the speed of sound of a gas can be determined by a conveniently compact and inexpensive device it can be provided in a small meter unit and provided with correspondingly compact means, preferably in the form of control electronics or a processing means, to produce the calorific value from the measured speed of sound. Such an apparatus to measure a calorific value of the gas is much smaller, cheaper and easier to operate than a conventional calorific value measuring device such as a chromatograph. Consequently, this enables the production of a meter to measure energy which is small, cheap and reliable when used with a means to measure a volume of gas supplied.
The calorific value of a gas is preferably measured by making a measure of a first thermal conductivity of the gas at a first temperature, making a measure of a second thermal conductivity of the gas at a second temperature which differs from the first temperature, and using the speed of sound and the first and second thermal conductivities in an operation producing the calorific value of the gas corresponding to said speed of sound and said first and second thermal conductivities.
The above described meter and method are suitable for both domestic and industrial use.
All references to the calorific value include parameters equivalent to calorific value such as Wobbe Index x{square root over (RD)}. All references to calorific value also include parameters dependent upon calorific value which when considered with the volume of gas supplied produce a parameter dependent upon the energy value.
All references to energy value include parameters dependent upon energy values such as cost in the local currency. The cost is determined by multiplying the consumed energy, measured in Joules or Watt hours for example, by the cost per unit of energy.